The use of water circulated through a cooling loop to cool fuel cell power plants is known in the prior art. When water is used to cool fuel cell power plants, such as those using acid electrolytes, the coolant entering the power section will be water which will be heated to a two phase water-steam mixture by the time it leaves the power section. The two phase mixture will then be taken to a steam separator where the steam component will be removed from the water component. When this separation occurs, the water will be stripped of entrained oxygen so that the water leaving the steam separator will generally contain from about 0 to about 50 ppb of oxygen. In most of these systems, makeup water is added to the loop in order to replace the water which is lost in the form of steam from the steam separator. U.S. Pat. No. 3,969,145 granted July 13, 1976 to P. E. Grevstad, et al discloses a cooling system which operates in the aforesaid manner. The foregoing system does make provisions for replacing water in the loop lost as steam, but it does not ensure that the amount of oxygen in the recirculating water will be within the desired range needed to provide good water chemistry and minimize corrosion in the system.
In order to achieve the desired fuel cell power plant water chemistry and minimize corrosion, the oxygen concentration in the water entering the power section should be in the range of about 50 to 150 ppb. Since the water leaving the steam separator is substantially devoid of oxygen, the makeup water is the only source of oxygen for the coolant prior to entering the power section. The amount of oxygen in the makeup water will be approximately 7,000 ppb. The rate at which the makeup water can be added to the loop cannot be varied however, since it must be enough to replace the water lost as steam from the loop. With the prior art system shown in U.S. Pat. No. 3,969,145 it will be apparent that the amount of oxygen in the water coolant as it reenters the power section is not controllable since the amount of makeup water needed is dictated by the amount of steam lost, and is thus not variable.